What is Loopback Interface in a Cisco Router

What is loopback interface in a Cisco Router?

A Loopback interface is a virtual interface which is logical and not like normal physical interfaces (Ethernet or Gigabit).

The loopback interface is really helpful as it is never down. It is popularly used in OSPF configurations where, the loopback IP address is used for OSPF Router ID. Since this loopback interface is always up, it is also used with BGP (Border Gateway Protocol). Even if there is some physical outbound interface is down, the logical interface (loopback) helps maintain the neighbor ship to be up.

The loopback interface is basically a software interface that acts similar to a physical interface where IP address can be assigned.

The loopback interface needs to be created manually on the router.

See the below output, there are no loopback interfaces.

no loopback interfaces

Now we will create a loopback interface, using the command “int loopback1”

int loopback1

Now we assign the IP address to the loopback interface, this is similar to assigning IP to a normal physical interface.

physical interface

We check again using “show ip int brief” and see the loopback created.

show ip int brief

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